19 April 2019

Whether they're idyllic floating cotton balls on an otherwise blue sky or ominous grey swirls that block the sun, clouds all begin as an invisible dot of water vapor. This elusive gas has been tricky to measure and track – until now. Research scientists at NASA's Langley Research Center in Hampton, Virginia, have created a new airborne instrument that can directly measure water vapor and floating particles in the atmosphere. The new data will help check the accuracy of satellite measurements, and improve weather and climate forecasts.

The instrument is called the High Altitude Lidar Observatory (HALO). It uses light detection and ranging (lidar), which works by shooting a pencil-thin laser beam through the atmosphere. Light from the pulsed laser bounces off molecules and particles suspended in the atmosphere, revealing what the human eye cannot see. The intensity of the signal reflected back to the lidar instrument gives the team the information they need to directly measure water vapor, as well as aerosol and cloud profiles.